The present invention relates to a gear box for a working machine, wherein the gear box has a friction disc clutch arrangement between a ring gear of a planetary gear set, connected to an output shaft of the gear box, and a gear box housing, wherein the gear box further comprises a control unit configured to control the friction disc clutch arrangement. The invention also relates to a corresponding method for controlling the gear box. The invention is applicable on working machines within the fields of industrial construction machines, in particular articulated haulers. Although the invention will be described with respect to an articulated hauler, the invention is not restricted to this particular machine, but may also be used in other construction equipment, or in other vehicles, such as a truck or similar.
In connection with transportation of heavy loads, a working machine in the form of an articulated hauler is frequently used. Such working machines may be utilized, for example for transports in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, an articulated hauler is frequently operated with large and heavy loads in rough terrain and on slippery ground where no regular roads are present.
An articulated hauler is a frame-steered working machine having a container for receiving and transporting a load. Such a working machine comprises a front section with a front frame and a first set of wheels, and a rear section with a rear frame and a second set of wheels. A pivot joint is arranged between the front section and the rear section allowing the front section and the section to pivot relative to each other about an axis extending in the vertical direction. Furthermore, the working machine comprises means for steering the working machine by pivoting the front section and the rear section relative to each other about the vertical pivot axis. The steering means normally includes a pair of hydraulic cylinders.
As described above, the articulated hauler is frequently used in rough terrain and as a consequence the different parts of the working machine have to be well dimensioned to be able to work properly in such environment. The gear box is a typical part of the articulated hauler which has to be dimensioned to handle heavy loading in combination with the rough terrain. An important aspect of the gear box is to have a relatively large step in gear ratios for both enabling driving in harsh terrain as well as driving at relatively high speeds on e.g., normal roads.
US 2010/0 029 433 discloses a powershiftable multistage transmission which, by splitting up the gear structure on a plurality of shaft lines, has a small overall length and being adaptable to different series of ratios and ratio steppings. Furthermore, the powershiftable multistage transmission has a brake arrangement in connection to the input shaft which may replace a traditional torque converter of the gearbox.
However, although the brake arrangement may replace a typical torque converter as well as being relatively small in size, the gearbox disclosed in US 2010/0 029 433 is in need of further improvements to be able to work more efficiently in e.g. the above mentioned rough terrain.
It is desirable to provide a gear box having improved functionalities in relation to prior art solutions.
According to a first aspect of the present invention there is provided a gear box for a working, machine, the gear box being arranged to be positioned in a first set of speed-changing gears and a second set of speed-changing gears, wherein the gear box comprises: a gear box housing, an input shaft configured to receive torque, and an output shaft for supplying torque out from the gear box, wherein the output shaft is connected to a planetary gear set of the gear box, a friction disc clutch arrangement which is arranged between a ring gear of the planetary gear set and the gear box housing for enabling connection of the ring gear to the gear box housing, and a control unit configured to controllably alternate the friction disc clutch arrangement between: an engaged state and an at least partially engaged state when the gear box is positioned in the first set of speed-changing gears, and between a disengaged state and an at least partially engaged state when the gear box is positioned in the second set of speed-changing gears.
By providing a gear box having a friction disc clutch arrangement according to the present invention, the need of the separate brake arrangement disclosed in the prior art may be reduced, thereby reducing the need of both as torque convener as well as the brake arrangement in connection to the input shaft. The positioning of the friction disc clutch arrangement may, in comparison to prior art solutions, level out gear changes occurring within the gear box, since the friction disc clutch arrangement is located “after” the gears in the gear box. Moreover, by controlling the friction disc clutch arrangement by means of the control unit, an increasing number of functionalities may be provided for the gear box. According to one advantageous example, when starting the working machine in a steep hill or the like, and the gear box is positioned in one of the speed-changing gears comprised in the first set of speed-changing gears, the control unit may then be configured to alternate the friction disc clutch arrangement between an engaged state and an at least partially engaged state in order to provide more energy to the gear box. Hereby, the friction disc clutch arrangement may be arranged to slip before running at normal gear, i.e. before being fully engaged, thereby providing a more robust behaviour with less risk of engine failure during vehicle start-up. Also, the control unit may be arranged to control the friction disc clutch arrangement such that it can balance torque variations and rotational speed variations in the gear box during operation by controllably providing the friction disc clutch arrangement in the at least partially engaged state, i.e. a slipping state, so that a relatively even and smooth driving characteristic of the gear box may be achieved. As a still further example, the friction disc clutch arrangement may also be used as a brake for the working machine when running the gear box at speeds where the friction disc clutch arrangement is normally positioned in a disengaged state, i.e. the second set of speed-changing gears. Hereby, changing the friction disc clutch arrangement between the disengaged state to the at least partially engaged state, i.e. a slipping state, will decelerate the articulated hauler. Accordingly, the friction disc clutch arrangement, in conjunction with the ordinary wheel brakes, will in such event reduce the speed of the articulated hauler.
Still further, the control unit may also control the friction disc clutch arrangement to be positioned in the at least partially engaged state when changing gear within the first or second sets of speed-changing gears.
Hereby, jerky motions of the gear box may be levelled out by the friction disc clutch arrangement.
The wording “engaged” should in the following and throughout the entire description be interpreted such that the ring gear of the planetary gear set is fixated to the gear box housing. Accordingly, the wording “at least partially engaged” should hence be interpreted such that the friction disc clutch arrangement is in a slipping state, i.e. it is neither fully engaged nor fully disengaged.
According, to an example embodiment, alternation between the first set of speed-changing gears and the second set of speed-changing gears may be controlled by engaging and disengaging the friction disc clutch arrangement, respectively.
Hereby, when running the gear box in the first set of speed-changing gears, the friction disc clutch arrangement is normally positioned in the engaged state. When running the gear box in the second set of speed-changing gears, the friction disc clutch arrangement is normally positioned in the disengaged state. Hence, a clear distinction of the difference between the first and second sets of speed-changing gears is defined for the gear box.
According to an example embodiment, the first set of speed changing gears comprises a plurality of lower speed-changing gears and the second set of speed-changing gears comprises a plurality of higher speed-changing gears, the lower speed-changing gears providing a lower rotational speed ratio of the output shaft in comparison to the higher speed-changing gears.
According to an example embodiment, the control unit may be further configured to acquire an input signal indicative of rotational speed and/or torque of the output shaft at a first point in time and to compare the rotational speed and/or torque at the first point in time with a rotational speed and/or torque of the output shaft at a second point in time, wherein the control unit is further configured to control the friction disc clutch arrangement based on the input signal and the comparison.
Hereby, the control unit may receive input regarding speed and/or torque variations of the output shaft and to control the friction disc clutch arrangement as a response to this input. The friction disc clutch arrangement may hence be controlled in such a way that e.g. torque variations can be levelled out in the gear box.
According to an example embodiment, the control unit may be further configured to alternate the friction disc clutch arrangement between either the engaged state and the at least partially engaged state or between the disengaged state and the at least partially engaged state if a difference in rotational speed and/or torque between the first point in time and the second point in time exceeds a predetermined threshold value.
Hereby, the gear box may be able to run relatively smoothly despite disturbances that might occur during operation since the friction disc clutch arrangement may continuously level out such disturbances by means of a braking- or slipping operation. Accordingly, variations of rotational speed and/or torque over time may also serve as an input for the control unit to determine when to position the friction disc clutch arrangement in an at least partially engaged state. The term “over time” can be a relative short time period, i.e. parts of a second, or a relative large time period, i.e. from a second to a few seconds, and up to several seconds.
According to an example embodiment, the control unit may be further configured to receive an input signal indicative of a temperature of the friction disc clutch arrangement and to controllably initiate supply of coolant to the friction disc clutch arrangement.
An advantage with this example embodiment is that the friction disc clutch arrangement may normally work as a dry clutch arrangement and receive coolant only when necessary. Hence, the friction disc clutch arrangement may work as a semi dry clutch. Accordingly, coolant may be supplied to the friction disc clutch arrangement when it is positioned in an engaged or at least partially engaged state. A temperature sensor or the like may be utilized to determine when coolant is necessary to be supplied.
However, the control unit may estimate the temperature by means of other parameters as well, such as measuring rotational speed of the friction elements in the clutch, estimation of applied pressure over time of the clutch in combination with input regarding the clutch temperature capacity, etc.
According to a second aspect of the present invention, there is provided a method for controlling a gear box, the gear box being arranged to be positioned in a first set of speed-changing gears and a second set of speed-changing gears, the gear box comprising a friction disc clutch arrangement arranged between a gear box housing of the gear box and a ring gear of a planetary gear set of the gear box for enabling connection of the ring gear to the gear box housing, the planetary gear set being coupled to an output shaft of the gear box for supplying torque out from the gear box, the method comprising the steps of acquiring an input signal indicative of an operational condition of the gear box; comparing the input signal with a predetermined set of rules; and alternating the friction disc clutch arrangement between an engaged state and an at least partially engaged state based on the input signal and the predetermined set of rules if the gear box is positioned in the first set of speed-changing gears, and alternating the friction disc clutch arrangement between a disengaged and an at least partially engaged state based on the input signal and the predetermined set of rules if the gear box is positioned in the second set of speed-changing gears.
Effects and features of this second aspect are largely analogous to those described above in relation to the first aspect of the present invention.
The friction disc clutch arrangement is hence configured to be controllably alternated between the engaged state, the at least partially engaged state, and the disengaged state based on a specific driving condition of the gear box. The input signal indicative of an operational condition may hence be interpreted as an input signal to the gear box providing information regarding driving conditions and/or gear box component behaviour. Gear box component behaviour should be interpreted as the behaviour of e.g. the clutches, shafts, gear wheels, etc. of the gear box.
According to an example embodiment, the input signal indicative of the operational condition of the gearbox may comprise information of change over time of rotational speed and/or torque of the output shaft.
Furthermore, the predetermined set of rules may comprise a predetermined threshold value of a difference in rotational speed and/or torque over time, and wherein the method further comprises the step of:
controllably alternating the friction disc clutch arrangement between either the engaged state and the at least partially engaged state or between the disengaged state and the at least partially engaged state if the difference in rotational speed and/or torque over time exceeds the threshold value.
Hereby, erratic behaviour of the articulated hauler may be substantially avoided since the gear box may be able to compensate for such behaviour by positioning the friction disc clutch arrangement in an at least partially engaged state.
According to an example embodiment, the predetermined set of rules may comprise as threshold value of a deceleration of the output shaft, and wherein the method further comprises the step of: positioning the friction disc clutch arrangement in the at least partially engaged state for the second set of speed-changing gears if the deceleration of the output shaft is below the threshold value.
When for example, the working machine is running at speeds where the friction disc clutch arrangement is positioned in a disengaged state and the working machine is starting to brake, the friction disc clutch arrangement may be positioned in the at least partially engaged state in order to further increase the braking efficiency of the working machine.
According to an example embodiment, the gear box is arranged in a working machine, wherein the predetermined set of rules further comprises a threshold value of a speed of the working machine, and wherein the method further comprising the steps of: alternating the friction disc clutch arrangement between the engaged state and the at least partially engaged state for the first set of speed-changing gears if the speed of the working machine is below the threshold value.
An advantage of the example embodiment is that if the speed of the working machine is below a predetermined minimum limit the friction disc clutch arrangement may be arranged to alternate between the engaged state and the least partially engaged state in order to provide a more robust behaviour of the vehicle and to avoid engine failure or erratic behaviour of the vehicle.
Furthermore, the input signal indicative of an operational condition may also comprise information regarding which gear that is currently being used in conjunction with the current speed and loading of the working machine. If, for example, the working machine is standing still and being empty of load, it might be beneficial to start from a stand still at a higher gear. In such a case it can be beneficial to position the friction disc clutch arrangement in an at least partially engaged state until the articulated hauler has reached a certain speed.
According to an example embodiment, the method may further comprise the steps of acquiring an input signal indicative of a temperature of the friction disc clutch arrangement; and supplying coolant to the friction disc clutch arrangement if the temperature is above a predetermined temperature limit.
According to an example embodiment, coolant may be supplied to the friction disc clutch arrangement when the friction disc clutch arrangement is positioned in the engaged state and/or the at least partially engaged state.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. For example, the above description of the different advantages of the present invention is only described in relation to driving the vehicle forward, the various embodiments of the invention are of course also applicable when providing the gear box in one of the reversed gears, i.e. when the working machine is driving backwards.